What are the grounds for patent opposition?

Any person prior to acceptance or after acceptance and grant of a patent may challenge the patent right on the ground of usurpation to the effect that the applicant for the patent has wrongfully obtained the invention or any part thereof by way of filching i.e. theft. Any person may initiate legal proceeding after the patent has been granted requesting revocation on the following grounds:

That the subject of the patent is not patentable within the terms as prescribed under the law. .

That the description of the invention or the claim or claims in the patent does not satisfy the requirements as prescribed under the law. .

That for the same invention, a patent has already been granted in the country as a result of a prior application or for an application benefiting from an earlier application.